there are also many patterns for hats that are knit flat. just look at the instructions and see if it tells you to "join without twisting" and if the instructions are in "rounds" or "rows."

if they are listed as rows then it is most often going to be knit flat. I have never done one flat because i LOVE knitting in the round (i almost always use circs though DPNs aren't that bad) but they can be done flat and then just seamed up.